Who is behind it and how do you know they are trustworthy? I wasn’t able to find much info but it seems it’s just some company (not a non profit / charity or anything). I know they have paid plans but it seems they also have an incentive or at least an ability to sell your purchase data?

Can you use a dummy address or a friend’s address in another country and/or sign up via a VPN to mask your location? There are companies that will open and scan your mail and make it available online so it could be a real address. But they are a little pricey. It’s likely due to UK laws not the provider themselves, so probably all reputable providers (that follow the law) may require it.

Maybe that’s specific to UK? I’ve never had to upload ID at any of the general domain registrars but am not in the UK. Maybe you’re looking for a registrar that doesn’t do that for UK residents, specifically. (or you might need to use a VPN or something, dunno)

Privacy aside most people tend to buy a domain at the cheapest registrar (keeping in mind whether to renew at that registrar later or transfer out to a new one when the time comes). There are domain registrar sites people use for comparison, been a bit since I’ve needed to shop around but sites like tld-list.com can be helpful. You could try doing a lookup there and work your way down the list until you find one you like.

Or if you’re really set on looking for a service that actually advertises no KYC then looking through this list may help kycnot.me/?categories=domains (njalla is one of the listed ones there as someone else mentioned).